Micromechanically-actuated reflectors are used as optical phase-shifting elements in several types of spatial light modulators, which function as image generators for applications such as image displays, printing, and maskless lithography. For example, the "Deformable Mirror Light Modulator" described in U.S. Pat. No. 4,441,791, and the "Enhanced Surface Deformation Light Modulator", U.S. Pat. No. 5,493,439, employ deformable membrane mirrors as light-modulating elements. Another prior-art device in this category, the "Flat Diffraction Grating Light Valve", U.S. Pat. No. 5,841,579, uses interdigitated groups of alternately fixed and movable ribbon reflectors to form a dynamically variable diffraction grating. Advantages of the grating light valve are that it can operate under high illumination levels and at very high (e.g., megahertz-level) switching rates, and it can be used with broadband illumination. This type of modulator is especially well adapted for display applications, but membrane-type modulators could have advantages for applications that require small pixels and very accurate control of the mirror deflection. For example, DUV lithography (at a 193 nm wavelength) would require maximum deflection amplitudes of approximately 50 to 75 nm, and at EUV wavelengths (e.g., 13 nm) the deflection amplitude would be only 3 to 5 nm. Modem film deposition technology can form membranes such as nitride film membranes with atomic-scale thickness control, making it possible to achieve very precisely-controlled membrane deflection characteristics for DUV or possibly EUV operation. Also, a membrane modulator pixel can be formed as a single, continuous reflector surface, in contrast to the grating light valve, which typically comprises six ribbon reflectors per pixel.